As illustrated in FIG. 6, it is a conventional practice to install a plurality of flood lights 1 around a building of historical note or a building serving as a landmark and to illuminate the exterior of the building with these devices during the night hours. This practice is commonly known as "light-up." A building which is lit in this manner appears as a clear silhouette in the nighttime sky, thus producing a picturesque landscape for those viewing the building from the surroundings.
However, when one within such a building (2) looks out from a window (3) during the light-up time, the light from a flood light may be incident on the eye. This may cause a glare or, in extreme cases, impair one's visual acuity.
To alleviate this phenomenon, it has been proposed that the angle of incidence with the normal be decreased by installing the flood light at the foot of the building. Alternatively, it has been proposed that the angle of incidence with the horizontal be decreased by installing the flood light sideways with respect to the window. However, if the angle of incidence is decreased, either with respect to the normal or with respect to the horizontal, the efficiency in lighting the building (the ratio of the brightness of the building to the projected light flux) tends to decrease, with the result that the freedom of choice in the angle of incidence with the normal or the horizontal was naturally limited.